aLIGO LHO Logbook

X1 SUS (SUS)

corey.gray@LIGO.ORG - posted 16:21, Wednesday 08 January 2025 - last comment - 08:36, Thursday 09 January 2025(82189)

Possible Laser Oddities for the LIGO SUS Fiber Puller

For reference here is a link with a summary of somewhat recent status for the LIGO SUS Fiber Puller: alog #80406

Fiber pulling was on a bit of a hiatus with a busy Fall/Winter of Ops Shifts and travel. This week, returned to the Fiber Puller lab to pull as many fibers as possible (have some free days this/next week). Thought I would note today's work because of some odd behavior.

Yesterday ended up spending most of the time making new Fiber Stock (we were down to 2, and about 12 more were made). Also packaged up Fiber Cartridge hardware returned from LLO and stored here to get re-Class-B-ed. Ended the day yesterday (Jan7) pulling 2025's first fiber: S2500002. This fiber was totally fine and no issues.

Today, I did some more lab clean-up but then around lunch I worked on pulling another fiber.

Issue with RESET Position

The first odd occurrence was with the Fiber Puller/Labview app. When I RESET the system to take a fresh new Fiber Stock, the Fiber Puller/Labview moved the Upper & Lower Stages to a spot where the Upper Stage/Fiber Cartridge Bracket was too "high" wrt the Fixed Lower Bracket---so I was not able to install a new Fiber Stock. Closing the Labview App, and a couple of "dry pulls" later, I was FINALLY! able to get the system to the correct RESET position. (not sure what was the issue here!)

Laser Power Looks Low

Now that the Fiber Stock was set to be POLISHED & PULLED, I worked on getting the Fiber Stock Aligned (this is a step unique to our set up here at LHO). As I put CO2 beam on the Fiber Stock, the first thing I noticed was very dim light on the stock (as seen via both cameras of the Fiber Puller). This was at a laser power of 55.5% (of the 200W "2018-new" laser installed for the Fiber Puller last summer). The alignment should not have changed for the system. I wondered if there were issues with the laser settings. I notice I had the laser controller at the "ANV" setting---it should be "MANUAL". But nothing improved the laser power.

Miraculously, the laser power (as seen with the cameras) returned to what I saw yesterday for S2500002, so I figured it was a glitch and then moved on to a POLISH, but within a few minutes and being mindful of the laser power on the stock on the cameras, once again the laser spot became dim. But I did nothing and just let the POLISH finish (about 15min). Fearing there was power-related issue, I decided to run the Pull (takes less than a minute), but at a higher power (75% vs 65% which had been the norm the last few months).

S2500003 pulled fine and passed.

I thought we were good, but when I set up for S2500004, I noticed more low and variable laser power. I worked on this fiber later in the afternoon after lunch. This one started with power which looked good to me (qualitatively), so I continued with set-up. But in a case of déjà vu, the laser power noticeably dipped in power as seen via the cameras. For this fiber I decided to continue, but since S2500003 had a "low-ish" violin fundamental freq (~498Hz), I figured I would return to a power of 65% for the Pull (hoping the laser power was hot enough for the pull (and not cool enough to cause the fiber to break during the pull---something which happened with our old and dying 100W laser we replaced in 2024).

Pulled the fiber and it all looked fine, profiled the fiber, and then ran an analysis on the fiber: it FAILED.

This is fine. Fibers fail. Since Aug we have pulled 29 fibers and this was the 5th FAIL we have had.

This is where I ended the day, but I'm logging this work only for some early suspicions with the laser. Stay Tuned For More!

Comments related to this report

corey.gray@LIGO.ORG - 08:36, Thursday 09 January 2025 (82200)

Link

Overall comments I wanted to add:

Want to have repeatability with the operation of this system, so if anything is odd it should be noted. For the most part we are hands off on the hardware of the Fiber Puller--the alignment should rarely need to be changed for many fiber pulls, and there is definitely no need to touch any of the mechanics of the machine. Our main interface with the machine is to load in a Fiber Stock, possibly make small adjustments of the upper translation stage, and that's about it for the machine. The rest of the handling is via the Labview program, laser controller, and switches which are outside of the Fiber Puller enclosure.
The RESET state issue is worth noting, because there had been minimal changes to the system from the afternoon before. The switches which control positions of the upper & lower moving stages had not been touched. Fiber Puller eventually resulted in a correct RESET state, but it was after several other "dry" pulls (and Labview restarts/checks).
The CO2 lasers for the Fiber Puller have some variability in laser power (which we see by the camera videos) and this is normal. Yesterday was notable only because the laser power was very noticeably low. The previous 100W laser (which was a bit older...manufactured in 2010) started to have symptoms of low power in 2021-22 which ultimately led to us decommissioning it and swapping it for the newer 200W laser (manufactured in 2018). Only noting the low-power observation as a data point for possible early end of life symptoms for it.